How to Read the Down Syndrome Screening Risk Cut Off
Down's syndrome (trisomy 21) can be diagnosed almost as soon as a baby is born, based on distinctive concrete characteristics that prompt immediate testing. Down's syndrome can likewise be diagnosed, or at to the lowest degree suspected, based on whatever of several prenatal tests including a nuchal translucency screening, sonogram, quadruple screen, or other blood tests. Here is how Down's syndrome is diagnosed in both scenarios.
Imaging
Modernistic imaging techniques tin provide very detailed pictures of what's going on inside of the body, including features of a yet-developing fetus. Since many characteristics of Downwardly syndrome are visible, it's possible to pick up on some of them in an ultrasound before a baby is built-in.
While imaging tests can help indicate the possibility of Downwardly syndrome, they cannot confirm it. Likewise, a negative test does not rule out Downwardly syndrome.
Nuchal Translucency Ultrasound Screening
This specialized ultrasound, which is performed at eleven to 13 weeks, measures the thickness of an area of tissue at the back of a fetus's cervix called the nuchal fold. Though this test is recommended for all pregnant women, this is a difficult measurement to obtain and only someone who has been specifically trained and certified to perform this screening can exercise it.
In general, a measurement under 3 millimeters (mm) is considered normal (or screen negative) and ane that'due south over three mm is considered aberrant (or screen positive). In the latter case, it will exist of import to meet with a genetic advisor to discuss your screening results, what they hateful, and your diagnostic testing options such equally chorionic villi sampling (CVS) or amniocentesis (run into beneath).
Ultrasound (Sonogram) Screening
Ultrasounds work past using audio waves to generate an image of the fetus. These waves pose no risk to mother or baby. The standard ultrasound is done between xviii and 22 weeks of pregnancy and can reveal a variety of physical characteristics that are associated with an increased risk that a developing babe has Downwardly syndrome.
The healthcare provider will rub a special gel on your abdomen and then slide a transducer, a wand-like apparatus that transmits sound waves into your abdomen, over your belly. The audio waves travel through the amniotic fluid, deflecting off of structures located in the uterus. The speed at which the waves bounce back differs depending on the density of what they hit. A reckoner turns this data into an paradigm of the fetus. The harder or denser a structure is, the brighter information technology will show up on the monitor.
Occasionally, but not always, infants with Downwards syndrome show subtle signs, called soft markers, on an ultrasound that suggest they may accept Downwards syndrome:
- A shorter-than-normal femur (thigh) os
- A missing nose bone in the commencement trimester
- Duodenal atresia: This abnormality of the duodenum, a part of the small-scale intestine, volition show upward on an ultrasound as a double chimera acquired past extra fluid and swelling in the duodenum and stomach. Duodenal atresia sometimes may be detected as early equally 18 to xx weeks, simply normally isn't seen until after 24 weeks. Another sign of duodenal atresia in pregnancy is excessive amniotic fluid. If a duodenal atresia shows up in an ultrasound, there is a 30% chance that the infant will have Down's syndrome.
- Sure middle defects
- Gastrointestinal blockages
These signs do not mean that a baby has Down syndrome for sure. Again, further testing is needed to confirm the diagnosis.
Also, it is important to note that most fetuses with Downward syndrome prove no abnormalities on ultrasound, which can exist falsely reassuring to parents who are especially concerned about this disorder.
Maternal Blood Tests
It's important to know that blood tests are used for screening and, like imaging tests for the condition, but signal the level ofpossibilitythat a kid has Down's syndrome.
Negative screening results mean that your chance of having a babe with Down's syndrome is low, just they exercise not guarantee there are no birth defects. If y'all have a negative event, you probable will not be offered follow-up diagnostic testing.
Positive screening results hateful the chances a fetus has Downward syndrome are higher than normal, and then follow-upwardly diagnostic testing volition exist offered. That said, most women with screen positive results will have normal healthy babies.
Quadruple Screen
This maternal blood test, which is part of routine prenatal care for all expectant moms, typically is performed between the 15th and 18th weeks of pregnancy. It measures levels of iv specific substances. Two of these happen to be associated with Down's syndrome:
- HCG (human chorionic gonadotropin):HCG is a hormone made by the placenta. In fact, very early in pregnancy, it's the substance used to discover pregnancy in home pregnancy tests, since it too shows up in urine. HCG levels in the claret of women carrying babies with Down syndrome tend to be higher than average.
- PAPP-A (pregnancy-associated plasma protein A): A woman with a low blood level of PAPP-A has an increased chance that her baby will have Down syndrome. Depression levels of PAPP-A also may indicate an increased risk for intrauterine growth restriction, premature delivery, preeclampsia, and stillbirth.
Prenatal Cell-Gratuitous DNA Screening (cfDNA)
This relatively new exam extracts Dna from both mother and fetus using a sample of the female parent's blood and screens for chromosome issues such as Down syndrome (too as trisomy 13 and trisomy 18). It tin can exist washed as early on in pregnancy as 10 weeks just is not routinely washed.
According to the American College of Obstetricians and Gynecologists (ACOG), healthcare providers will recommend cfDNA only for women with certain risk factors for fetal defects, including advanced maternal age (35 or over); a fetal ultrasound that shows an increased chance of chromosome abnormality; a previous pregnancy with a trisomy; a positive first- or second-trimester maternal screening test; or a known counterbalanced chromosome translocation in the female parent or male parent.
It'south important to understand that cfDNA testing can but indicate if a fetus is at an increased run a risk for a chromosome trouble or is unlikely to have 1. It is non a diagnostic test. It also is expensive, although the test may be covered past health insurance for women of advanced maternal age.
While these screenings tin can exist helpful, the only way to definitively diagnose Down syndrome is to get a diagnostic test.
Diagnostic Tests
If a prenatal screening test indicates there's a possibility your child will take Down syndrome or if you have risk factors for having a child with the disorder, then you may exist faced with taking the next step and confirming the diagnosis. This is an extremely personal determination, 1 that'due south fraught with dueling emotional and practical implications.
Deciding Whether to Have a Confirming Exam
It can be helpful to ask yourself very specific questions near whether prenatal testing to confirm a diagnosis of Downwards syndrome (or any nativity defect) is the right thing for you and your family. For case, you'll desire to consider your own personality: Practice you lot handle things better when you know what to expect? Or would knowing that yous're conveying a kid with trisomy 21 cause you overwhelming anxiety?
In businesslike terms, would knowing ahead of fourth dimension allow you lot to ready for the potential health problems your baby with Downward syndrome may be born with? And, as hard as this scenario is to think nearly, would learning you accept a kid with a nascence defect cause you to consider terminating the pregnancy?
Be open about your thoughts when speaking with your healthcare provider and know that getting a diagnostic test is entirely your choice.
Down Syndrome Physician Discussion Guide
Become our printable guide for your next healthcare provider's appointment to help you ask the right questions.
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Karyotyping
If you decide to motility forrard with diagnostic testing, amniocentesis and chorionic villi sampling volition exist offered to you. Tissue retrieved with either of these procedures will exist karyotyped.
A karyotype is an analysis of a infant's genetic makeup that looks at the number of chromosomes he or she has under a microscope.
Under normal circumstances, there are 46 chromosomes organized in 23 pairs. Chromosome pairs are numbered one through 23. In the case of Downwardly syndrome, at that place is an extra chromosome in the 21st spot, meaning there are three of this particular chromosome. (This is why the clinical proper noun for Down syndrome is trisomy 21.)
A karyotype can be done using most any type of cell. When a diagnosis is being confirmed subsequently nativity, for example, the cells ordinarily are taken from a sample of the babe's blood. During pregnancy, karyotyping can be done by performing one of the following tests. Neither of these is considered a routine role of prenatal care, although they often are recommended for women who are 35 or over or who have other risk factors for having a child with a chromosomal abnormality.
- Amniocentesis:This exam, which is done between weeks 15 and 20 of pregnancy, creates a karyotype using a sample of amniotic fluid. A healthcare provider uses an ultrasound to help guide a long, thin needle into a woman's abdomen and through to the uterus in guild to extract a sample of fluid from the amniotic sac. This fluid contains pare cells that have sloughed off of the fetus, which will then be tested.
It takes just a few moments to extract amniotic fluid, but most women do report feeling some discomfort and balmy cramping. Amniocentesis is relatively safe: It carries a i-in-400 chance of causing miscarriage. The process of culturing the cells so that they can be karyotyped tin can take upwardly to 2 weeks. - According to the National Down syndrome Gild (NDSS), the test is nearly 100 pct accurate in diagnosing Down's syndrome prenatally. What'southward more, it can distinguish between complete trisomy 21, translocation Down syndrome, and mosaic Downward syndrome.
- Chorionic Villi Sampling (CVS):As with amnio, CVS testing uses karyotyping to diagnose Down syndrome. However, the cells examined are taken from structures in the placenta chosen chorionic villi.
CVS is performed at 11 to 13 weeks of pregnancy and is done in 1 of 2 ways: Either a needle is inserted directly into the abdomen or is threaded through the cervix (much like having a Pap smear). - The insertion of the needle can be painful, only the procedure is very quick. CVS poses the same modest risk of miscarriage as amniocentesis, is nearly 100 percent authentic, and is able to reveal which type of trisomy 21 a baby has. It usually takes a couple of weeks for full results from CVS testing to be finalized.
FISH Testing
Fluorescent in situ hybridization (FISH testing or FISH analysis) is a relatively new technique that tin can determine how many copies of a particular chromosome a cell has. It's unremarkably done using the same tissue sample from an amniocentesis or CVS test.
To perform a FISH assay, colored dyes are used to highlight sure chromosomes, which makes it possible to count them. One advantage of using FISH analysis rather than karyotyping is that it isn't necessary to culture cells earlier analyzing them. This ways results tin can be available in a few days rather than a few weeks.
A disadvantage of FISH is that dissimilar karyotyping, it merely can reveal if there is an extra chromosome 21. It doesn't offer information about the structure of the chromosomes that would exist needed to identify Down's syndrome as complete, mosaic, or translocation trisomy 21. The differences in these types touch on the severity of the condition and the likelihood of conceiving some other child with Down syndrome.
Physical Examination
Down syndrome is unremarkably quite evident every bit soon as a baby with the disorder is built-in, every bit many of its distinctive physical characteristics are present at birth. These include:
- A round face with a flat profile and pocket-size facial features (nose, mouth, ears, and optics)
- Protruding natural language
- Almond-shaped upturned eyes with epicanthus folds
- White flecks in the colored part of the eyes (Brushfield spots)
- A short cervix and a minor head that'south somewhat flat in the back (brachycephaly)
- A single crease beyond the palm of each hand (ordinarily at that place are two), short stubby fingers, and a pinky finger curves inward—a condition chosen clinodactyly
- Small feet with a larger than normal space between the big and second toes
- Hypotonia, or low muscle tone, which causes the newborn to appear "floppy" due to a condition chosen hypotonia.
These characteristics are red flags that a newly born babe has Down syndrome. To ostend the diagnosis, a blood sample volition be taken and used to create a karyotype.
Source: https://www.verywellhealth.com/diagnosing-down-syndrome-1120396
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